The long term goals of our laboratory are to study the transport properties of the blood retinal barrier (BRB) under both normal and pathological conditions. The proposed research represents an extension of our work on glucose transport across the BRB and the initiation of studies into amino acid transport. Since the pigment epithelium (PE) constitutes a major component of the BRB, much of our work is focused on this tissue. Previous work has suggested that two carrier mediated sugar transport systems are in operation at the level of the PE - one of which is phloretin sensitive. We will attempt to determine if these apparently different transport systems are preferentially distributed on the apical and basal sides of the pigment epithelium. The extension of the glucose transport studies will utilize bovine PE tissue mounted as a membrane in a chamber. Studies on amino acid transport across the PE will be initiated to determine the unidirectional flux for representatives of the neutral, basic and acidic groups of amino acids. In addition, ionic dependence and the effects of metabolic inhibitors on amino acid transport will be investigated. Competition studies for common transport sites among amino acids will also be performed. The amino acid transport studies across the PE will also employ the bovine PE tissue mounted as a membrane in a chamber. Information on the transport properties of the BRB is vital to our understanding of such pathological conditions as diabetic retinopathy where an increased permeability of the BRB is the earliest ocular defect noted.